1. Field of the Invention
Parasitic mites are serious pests affecting honey bee populations worldwide. Both Varroa jacobsoni and the tracheal mite Acarapis woodi have been identified as the cause of infestations resulting in an extensive reduction in honey bee populations. This population reduction has had serious consequences in agriculture, since honey bees are critical to pollination in the fields and thus to the successful production of many crops. Although various treatments have been attempted, many have been unsuccessful due in large part to the toxicity of the chemicals utilized or to difficulties in registration with environmental agencies. Only one product is currently registered in the United States for control of Varroa: Apistan.RTM. (Wellmark International, Dallas, Tex.), a plastic strip containing fluvalinate. Tracheal mites can be controlled with menthol or, less effectively, by use of vegetable oil patties placed in the hive. None of these materials is active against both parasitic mites, however, and the use of only a single registered product is conducive to the development of resistance. There has thus been a strong incentive to develop a product which will provide safe and effective protection for honey bees over existing treatments.
2. Description of the Related Art
Formic acid has been used in liquid form in Europe and Canada and has been shown to control parasitic mites of honey bees in a wide variety of situations. The first comprehensive report on such use of formic acid appeared in a special issue on varroatosis (Ritter and Ruttner. 1980. Allg. Dtsch. Imkerztg. vol. 14, pp. 151-155). Subsequently, the "Illertisser Mite plate" (IMP), a cardboard-like material that could be soaked with formic acid and placed in the hive was developed (Wachendorfer et al. 1985. Apidologie. vol. 16, pp. 291-305). This method, or modifications of it, was tested against parasitic bee mites in a number of countries, including Germany (Hoppe et al. 1989. Amer. Bee J. vol 129, pp. 739-742), Sweden (Fries, I. 1989. Swedish J. Agric. Res. vol. 19, pp. 213-216) and Dubai (Bracey and Fisher. 1989. Amer. Bee J. vol. 129, pp. 735-737) Other known application methods have included soaked cheesecloth (Liu and Nasr. 1992. Amer. Bee J. vol. 132, pp. 666-668) and containers with wicks (Sharma et al. 1983. Indian Bee J. vol. 45, pp. 1-2; Lupo and Gerling. 1990. Apidologie. vol. 21, pp. 261-267). Nelson et al. (1994. Bee Science. vol. 3, no. 3, pp. 129-134) disclosed formic acid application for controlling tracheal mites and compared treatments using liquid formic acid, formic acid gel-strips, menthol-paste and the German product IMP. Most of these methods use varying concentrations of dilute liquid formic acid, and most require multiple applications. In addition, use of the IMP apparatus necessitates the removal of part of the honeycomb from the hive to meet space requirements.
Formic acid is very corrosive and dispensing it inside the beehive has been problematic. The current methods require handling liquid formic acid, frequent applications and/or extensive hive manipulation. Due to its hazardous nature, the development of a formic acid formulation that was both safer than a liquid and had the advantage of fewer applications was desirable.
Furthermore, an increase in resistance by Varroa to the fluvalinate-containing control product over several years in Europe, and the expectation that such resistance is inevitable elsewhere, has provided an additional incentive for the development of a useful formic acid formulation. By having an additional effective treatment available and the capability of alternating treatments, such resistance can at least be delayed and possibly avoided altogether.